Seres Therapeutics names co-CEOs as current chief executive steps down

Seres Therapeutics Inc. (NASDAQ: MCRB) announced Thomas DesRosier and Marella Thorell will serve as co-chief executive officers following Eric Shaff's departure on July 31, 2025. Shaff will remain on the company's board of directors after stepping down from his CEO role.

DesRosier currently serves as chief legal officer and Thorell as chief financial officer. Both executives will retain their existing responsibilities alongside their new co-CEO roles. Shaff has led the company for a decade.

The Cambridge, Massachusetts-based biotherapeutics company stated it is engaging with multiple parties regarding various deal structures, including potential business development partnerships, to secure additional capital and resources for clinical advancement of its drug candidates.

Seres is developing SER-155, which received breakthrough therapy designation from the FDA for reducing bloodstream infections in adults undergoing allogeneic hematopoietic stem cell transplant. A Phase 1b study showed SER-155 reduced bloodstream infections by 77% compared to placebo in this patient population.

DesRosier joined Seres in 2016 and previously held senior legal positions at ARIAD Pharmaceuticals, Cubist Pharmaceuticals, Sanofi and Genzyme Corporation. Thorell joined the company in March 2024 and has over 25 years of finance and operations experience, including previous roles at Evelo Biosciences and Centessa Pharmaceuticals.

The company sold its FDA-approved oral microbiome therapy VOWST to Nestlé Health Science in September 2024. Seres continues to develop live biotherapeutics for medically vulnerable patient populations.

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